Wafer carrier and chemical mechanical polishing apparatus including the same

ABSTRACT

Disclosed are a wafer carrier assembly and a chemical mechanical polishing apparatus including the same. The present wafer carrier for a chemical mechanical polishing apparatus comprises: a wafer carrier head rotatably mounted on the apparatus, having a lower surface for contacting a wafer; a retaining ring attached to the lower surface of the wafer carrier head, for retaining or preventing the wafer from moving from the wafer carrier head during rotational motion thereof; and a guard ring attached to the lower surface of the wafer carrier head a distance outside the retaining ring.

This application claims the benefit of Korean Application No. 10-2005-0039779, filed on May 12, 2005, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for chemical mechanical polishing of a semiconductor wafer. More specifically, the present invention relates to a wafer carrier assembly for use in a chemical mechanical polishing apparatus.

2. Description of the Related Art

Chemical-mechanical polishing (CMP) process plays an important role in high-integration and ultraminiaturization of a semiconductor device. Typically, a semiconductor device including high density circuits requires closely spaced multilevel metallization lines. Thus, a poor surface planarity of a semiconductor wafer exerts a bad influence upon interconnection between metallization lines. CMP technology has been developed as demand for a global planarization of a semiconductor wafer to miniaturize a circuit dimension.

CMP removes material from the surface of the wafer by chemical and mechanical action(s), in the production of ultra-high density integrated circuits. In a typical CMP process, the top layer of the wafer is exposed to an abrasive medium under controlled chemical, pressure, velocity, and temperature conditions. Conventional abrasive media include slurries and polishing pads.

FIG. 1 shows a perspective view of a conventional CMP apparatus. Referring to FIG. 1, CMP apparatus 10 utilizes a mechanical working of polishing pad 12 and a chemical working of slurry 15 to polish a surface of a wafer. Polishing pad 12 is attached on polishing table or turntable 11, and slurry 15 is supplied on polishing pad 12 by slurry providing unit 14. A wafer is contained or arranged in wafer carrier head 13. Here, turntable 11 is simply rotated, but wafer carrier head 13 is rotated and a downward force is applied by wafer carrier support frame 13 a. In general, a wafer is fastened to wafer carrier head 13 by a ceramic material of carrier ring 20. A wafer contacts polishing pad 12 by a load of wafer carrier head 13 and a pressure of wafer carrier support frame 13 a. As slurry 15 moves between a wafer and polishing pad 12, material is removed from the top layer of the wafer mechanically by the abrasive particles in slurry solution 15 and/or surface protrusions of polishing pad 12, and chemically by the chemicals in slurry solution 15.

Meanwhile, in such CMP process, the surface of the wafer to be polished closely contacts with polishing pad 12. Accordingly, the distribution of pressure between the wafer and polishing pad 12 affects the resultant surface planarity of the wafer. Especially, when carrier ring 20 for fastening the wafer weighs down polishing pad 12 by a pressure of wafer carrier support frame 13 a, unwanted ripples may be generated on polishing pad 12, owing to the pad bounding effect.

Specifically, referring to FIG. 2, as carrier ring 20 presses polishing pad 12, a portion of polishing pad 12 protrudes in the vicinity of the edges of carrier ring 20. In general, carrier ring 20 is formed of ceramic material, but polishing pad 12 is formed of elastic material. Therefore, when carrier ring 20 presses polishing pad 12, polishing pad 12 is partially deformed so that a ripple 12 a occurs in the vicinity of carrier ring 20. The pressure applied to the edge of wafer, near the ripples 12 a, is much larger than that applied to the center of wafer. In other words, a polishing rate of the edge of wafer is relatively increased, comparing with that of the center of wafer. As a result, the polished surface of wafer becomes uneven or non-uniform, which may decrease the yield of semiconductor devices from the wafer.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a wafer carrier assembly and a chemical mechanical polishing apparatus including the same, which can prevent a periphery of a semiconductor wafer from being overpolished during a chemical mechanical polishing process, owing to the deformation of polishing pad.

To achieve the above objects, an embodiment of a wafer carrier for use in a chemical mechanical polishing apparatus, according to the present invention, comprises: a wafer carrier head rotatably mounted on the apparatus, having a lower surface adapted for contacting a wafer; a retaining ring attached to and/or extending from the lower surface of the wafer carrier head, for retaining the wafer on the wafer carrier head during rotational motion thereof; and a guard ring attached to and/or extending from the lower surface of the wafer carrier head, a distance outside of the retaining ring.

Especially, in the wafer carrier according to the present invention, an inner wall of the retaining ring is in contact with a periphery of the wafer. In addition, a protrusion height of the guard ring is substantially equal to or larger than that of the retaining ring, relative to a surface of or thickness of the wafer. Moreover, a bottom surface of the retaining ring is arranged on substantially the same plane as a polished surface of the wafer. Preferably, the wafer carrier further includes a resilient member positioned between the lower surface of the wafer carrier head and the wafer.

In addition, a chemical mechanical polishing apparatus according to the present invention comprises: a turntable rotated by a driving means; a polishing pad positioned on an upper surface of the turntable; a wafer carrier support frame; a wafer carrier rotatably mounted on the wafer carrier support frame, for containing a wafer to be arranged opposite the polishing pad; and a slurry providing unit configured to provide a slurry on an upper surface of the polishing pad. Here, the wafer carrier includes: a wafer carrier head having a lower surface adapted to contact a wafer; a retaining ring attached on and/or extending from the lower surface of the wafer carrier head, for retaining the wafer during rotational motion; and a guard ring attached to and/or extending from the lower surface of the wafer carrier head a distance outside of the retaining ring.

These and other aspects of the invention will become evident by reference to the following description of the invention, often referring to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a conventional CMP apparatus.

FIG. 2 is a cross-sectional view of a conventional CMP apparatus, especially illustrating a wafer carrier assembly and a turntable on which a polishing pad is arranged.

FIG. 3 is a cross-sectional view of an embodiment of a wafer carrier assembly according to the present invention, including a retaining ring and guard ring.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 illustrates a cross-sectional view of an embodiment of a wafer carrier assembly including a carrier ring comprising a retaining ring 22 and guard ring 24, according to the present invention. Wafer carrier head 13 is rotated and forced downwardly by wafer carrier support frame 13 a during a polishing process. A wafer, referred to as W, is arranged on a lower surface of wafer carrier head 13. Additionally, a resilient member (e.g., a backing film, not shown) can be positioned between the lower surface of wafer carrier head 13 and the wafer W. Especially, wafer carrier head 13 can be equipped with means for applying vacuum to the wafer, for the purpose of firmly holding the wafer.

The present invention includes retaining ring 22 and guard ring 24 as a carrier ring. Here, retaining ring 22 may function to fasten the wafer to wafer carrier head 13, and it is attached on the lower surface of wafer carrier head 13. Retaining ring 22 retains the wafer W, or prevents the wafer from moving or departing outwardly, during the rotational motion of the wafer carrier head 13. Preferably, retaining ring 22 has a substantially annular form that can be adjustable to the periphery of the wafer. More preferably, an inner wall 22 a of retaining ring 22 may be arranged to be in contact with the periphery of the wafer, thus effectively preventing the departure of the wafer from wafer carrier head 13. In addition, a bottom surface of retaining ring 22 is preferably in substantially the same plane as a polished surface of the wafer. In other words, it is preferable to minimize the clearance and/or the compression between the bottom surface of retaining ring 22 and polishing pad 12. When the clearance is too large, the wafer may depart from wafer carrier head 13 through a gap between retaining ring 22 and polishing pad 12. When the compression is too great, a ripple may form inside of the retaining ring 22 and overpolish en edge region or periphery of the wafer. Thus, retaining ring 22 is preferably configured to have a thickness substantially equal to the thickness of the wafer and (if present) any resilient member or backing film on the wafer carrier head 13.

Guard ring 24 is attached on the lower surface of wafer carrier head 13, a predetermined distance from retaining ring 22. In other words, the inside diameter of guard ring 24 is larger than the outside diameter of retaining ring 22. The present invention includes guard ring 24 as another carrier ring, as well as retaining ring 22 for fastening the wafer. Thus, two carrier rings (i.e., retaining ring 22 and guard ring 24) generally work together to prevent the periphery of the wafer from being overly polished due to the deformation of polishing pad 12. The deformation of polishing pad 12 mostly occurs in the vicinity of guard ring 24, particularly when guard ring 24 has a thickness such that its lower surface extends slightly beyond the bottom surface of retaining ring 22. Therefore, polishing pad 12 rarely deforms in the vicinity of retaining ring 22 and the wafer.

More specifically, as shown in FIG. 3, when wafer carrier head 13 is forced down by wafer carrier support frame 13 a, guard ring 24 primarily presses down polishing pad 12. As a result, the protrusion portion 12 a of polishing pad 12, owing to the pad bounding effect or deformation of the pad, occurs intensively in the vicinity of guard ring 24. In this case, the pad bounding phenomenon rarely occurs in the vicinity of retaining ring 22 and the wafer, thus the pressure working on the wafer becomes uniform over the periphery and the center of the wafer. Therefore, the polishing rates according to the chemical and mechanical polishing actions can be maintained constantly over the entire surface of the wafer.

Meanwhile, a gap (referred to as G) between retaining ring 22 and guard ring 24 can be determined or controlled, based on the elasticity of polishing pad 12, to minimize the pad bounding effect on the wafer. In the case where the polishing pad material has a large elasticity, a region where the pad bounding phenomenon occurs may be wide. In this case, the gap G is preferably relatively large for the pad bounding region not to reach the wafer. In addition, forming a width W1 of guard ring 24 larger than a width W2 of retaining ring 22 can minimize the extent of polishing pad's deformation in the inner region of guard ring 24.

It is preferable to form a protrusion height H of guard ring 24 larger than or equal to a protrusion height h of retaining ring 22, in order to concentrate the pad bounding phenomenon in the vicinity of guard ring 24. In the case where the protrusion height h of retaining ring 22 is larger than the protrusion height H of guard ring 22, the pad bounding phenomenon may occur in the vicinity of retaining ring 22. On the other hand, if the protrusion height H of guard ring 24 is unacceptably larger than the protrusion height h of retaining ring 22, the wafer may become out of close contact with polishing pad 12. Accordingly, it is preferable to appropriately control the protrusion heights of retaining ring 22 and guard ring 24. Here, the protrusion height H or h is defined as a height based on a top surface of the wafer or the lower surface of wafer carrier head 13 in contact with the top surface of the wafer, not a real or actual height of retaining ring 22 or guard ring 24. In one embodiment, the difference in the protrusion heights of (H−h) retaining ring 22 and guard ring 24 is less than the height of pas protrusion 12 a under one or more given sets of polishing conditions (e.g., the downward force applied by wafer carrier head 13, the elasticity and/or compressibility of polishing pad 12, the width of gap G, the width[s] of retaining ring 22 and/or guard ring 24, and/or the amount of and/or formulation of the slurry, etc.).

The wafer carrier assembly, according to the present invention, includes a retaining ring for retaining a semiconductor wafer, and a guard ring as an additional carrier ring. The pad bounding phenomenon is generally concentrated in the vicinity of the guard ring. In other words, when the pad bounding phenomenon is prevented in the vicinity of the wafer, a pressure applied to the wafer can be maintained constantly and uniformly over an entire surface of the wafer to be polished. Therefore, a CMP apparatus including a wafer carrier assembly according to the present invention can prevent a periphery or edge region of a wafer from being overly polished, because a polishing rate is uniform over an entire surface of a wafer. As a result, the yield and reliability of semiconductor devices can be improved (in some cases, significantly so).

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A wafer carrier for a chemical mechanical polishing apparatus, comprising: a wafer carrier head rotatably mounted on the apparatus, having a lower surface adapted for contact with a wafer; a retaining ring extending from the lower surface of the wafer carrier head, for retaining the wafer on the wafer carrier head during rotational motion thereof; and a guard ring extending from the lower surface of the wafer carrier head a distance outside of the retaining ring.
 2. The wafer carrier of claim 1, wherein an inner wall of the retaining ring is configured for contact with a periphery of the wafer.
 3. The wafer carrier of claim 1, wherein a protrusion height of the guard ring is substantially equal to or greater than that of retaining ring.
 4. The wafer carrier of claim 2, wherein a protrusion height of the guard ring is substantially equal to or greater than that of retaining ring.
 5. The wafer carrier of claim 1, wherein a protrusion height of the guard ring is greater than that of the retaining ring, relative to a surface of the wafer.
 6. The wafer carrier of claim 2, wherein a protrusion height of the guard ring is greater than that of the retaining ring, relative to a surface of the wafer.
 7. The wafer carrier of claim 1, wherein a bottom surface of the retaining ring is on substantially a same plane as a polished surface of the wafer.
 8. The wafer carrier of claim 2, wherein a bottom surface of the retaining ring is on substantially a same plane as a polished surface of the wafer.
 9. The wafer carrier of claim 1, further comprising a resilient member on the lower surface of the wafer carrier head.
 10. A chemical mechanical polishing apparatus, comprising: a rotatable turntable; a polishing pad on an upper surface of the turntable; a wafer carrier support frame; a wafer carrier rotatably mounted on the wafer carrier support frame, including (i) a wafer carrier head having a lower surface adapted for contacting a wafer, (ii) a retaining ring on the lower surface of the wafer carrier head, for retaining the wafer on the wafer carrier head, and (iii) a guard ring extending from the lower surface of the wafer carrier head a distance outside the retaining ring; and a slurry providing unit for providing a slurry on an upper surface of the polishing pad.
 11. The apparatus of claim 10, wherein an inner wall of the retaining ring is configured for contact with a periphery of the wafer.
 12. The apparatus of claim 10, wherein a protrusion height of the guard ring is substantially equal to that of retaining ring.
 13. The apparatus of claim 11, wherein a protrusion height of the guard ring is substantially equal to that of retaining ring.
 14. The apparatus of claim 10, wherein a protrusion height of the guard ring is greater than that of the retaining ring, relative to a surface of the wafer.
 15. The apparatus of claim 11, wherein a protrusion height of the guard ring is greater than that of the retaining ring, relative to a surface of the wafer.
 16. The apparatus of claim 10, wherein a bottom surface of the retaining ring is on substantially a same plane as a polished surface of the wafer.
 17. The apparatus of claim 10, wherein a bottom surface of the retaining ring is on substantially a same plane as a polished surface of the wafer.
 18. The apparatus of claim 11, wherein the wafer carrier further includes a resilient member positioned on the lower surface of the wafer carrier head.
 19. A method of polishing a wafer, comprising the steps of: providing a slurry on an upper surface of a polishing pad on an upper surface of a turntable; and polishing a wafer on the polishing pad, wherein the wafer is retained by a retaining ring on a lower surface of a wafer carrier head, the wafer carrier head further including a guard ring extending from the lower surface of the wafer carrier head a distance outside the retaining ring.
 20. The method of claim 19, wherein the guard ring has a protrusion height greater than or equal to that of the retaining ring, relative to a surface of the wafer. 